}

    @Override
    public SortedSet<E> subSet(E fromElement, E toElement) {
      synchronized (mutex) {
        return sortedSet(delegate().subSet(fromElement, toElement), mutex);
      }
    }

    @Override
    public SortedSet<E> headSet(E toElement) {
      synchronized (mutex) {
        return sortedSet(delegate().headSet(toElement), mutex);
      }
    }

    @Override

    }

    @Override
    public SortedSet<E> subSet(E fromElement, E toElement) {
      synchronized (mutex) {
        return sortedSet(delegate().subSet(fromElement, toElement), mutex);
      }
    }

    @Override
    public SortedSet<E> headSet(E toElement) {
      synchronized (mutex) {
        return sortedSet(delegate().headSet(toElement), mutex);
      }
    }

    @Override

      BoundType fromBoundType,
      @ParametricNullness E toElement,
      BoundType toBoundType) {
    // These are checked elsewhere, but NullPointerTester wants them checked eagerly.
    checkNotNull(fromBoundType);
    checkNotNull(toBoundType);
    return tailMultiset(fromElement, fromBoundType).headMultiset(toElement, toBoundType);
  }

  abstract Iterator<Entry<E>> descendingEntryIterator();

    }

    @Override
    public String toString() {
      return standardToString();
    }

    @Override
    public SortedSet<T> subSet(T fromElement, T toElement) {
      return standardSubSet(fromElement, toElement);
    }
  }

  @AndroidIncompatible // test-suite builders
  public static Test suite() {
    TestSuite suite = new TestSuite();

      return new FilteredSortedSet<>(
          ((SortedSet<E>) unfiltered).subSet(fromElement, toElement), predicate);
    }

    @Override
    public SortedSet<E> headSet(@ParametricNullness E toElement) {
      return new FilteredSortedSet<>(((SortedSet<E>) unfiltered).headSet(toElement), predicate);
    }

    @Override

  @Override
  public SortedMultiset<E> subMultiset(
      E fromElement, BoundType fromBoundType, E toElement, BoundType toBoundType) {
    // These are checked elsewhere, but NullPointerTester wants them checked eagerly.
    checkNotNull(fromBoundType);
    checkNotNull(toBoundType);
    return tailMultiset(fromElement, fromBoundType).headMultiset(toElement, toBoundType);
  }

  abstract Iterator<Entry<E>> descendingEntryIterator();

    throw new NoSuchElementException();
  }

  @Override
  ContiguousSet<C> headSetImpl(C toElement, boolean inclusive) {
    return this;
  }

  @Override
  ContiguousSet<C> subSetImpl(
      C fromElement, boolean fromInclusive, C toElement, boolean toInclusive) {
    return this;
  }

  @Override
  ContiguousSet<C> tailSetImpl(C fromElement, boolean fromInclusive) {

      BoundType fromBoundType,
      @ParametricNullness E toElement,
      BoundType toBoundType) {
    // These are checked elsewhere, but NullPointerTester wants them checked eagerly.
    checkNotNull(fromBoundType);
    checkNotNull(toBoundType);
    return tailMultiset(fromElement, fromBoundType).headMultiset(toElement, toBoundType);
  }

  abstract Iterator<Entry<E>> descendingEntryIterator();

      return new FilteredSortedSet<>(
          ((SortedSet<E>) unfiltered).subSet(fromElement, toElement), predicate);
    }

    @Override
    public SortedSet<E> headSet(@ParametricNullness E toElement) {
      return new FilteredSortedSet<>(((SortedSet<E>) unfiltered).headSet(toElement), predicate);
    }

    @Override

    @Override
    ImmutableSortedSet<C> headSetImpl(C toElement, boolean inclusive) {
      return subSet(Range.upTo(toElement, BoundType.forBoolean(inclusive)));
    }

    @Override
    ImmutableSortedSet<C> subSetImpl(
        C fromElement, boolean fromInclusive, C toElement, boolean toInclusive) {
      if (!fromInclusive && !toInclusive && Range.compareOrThrow(fromElement, toElement) == 0) {
        return ImmutableSortedSet.of();